When writing on a whiteboard it's annoying to a) hold the cap in hand all the time or b) look for the cap when finished and c) find parched pens on the tray. Nobody puts the traditional loose caps on the pen during a presentation. With the suction cup nearby it's just a flick of the wrist.

The whiteboard markers with the suction cup are always at hand. It's easy to pick the pen protruding horizontally (on a board) or vertically (on a desk). Perhaps - we could prevent the marker from falling by having the suction lid point upwards (45 degrees?). The suction cups may be sold complete with markers, or by themselves, ready to accept the purchaser's own pens with a simple universal push fit. We should color tint the suction cups.